1. Field of the Invention
The present invention relates generally to an arrangement, including a method and system, for producing images based upon diffusional wave theory and frequency domain analysis. A medium to be imaged is illuminated with amplitude modulated radiation, and radiation transmitted or reflected by the medium is detected at a plurality of detection locations, as by a television camera. The phase and also the amplitude demodulation of the radiation is detected, and a relative phase image and also a demodulation amplitude image of the medium are generated from respectively the detected relative phase values and the detected demodulation amplitudes of the radiation at the plurality of locations.
The present invention is particularly suited for medical applications for generating images of internal anatomical details of the body using a rear infrared amplitude modulated source for illumination and a television camera with a modulated image intensifier as a detector. In greater detail, the subject invention pertains to an arrangement as described which is capable of real-time imaging of thick tissues with a resolution of a few millimeters, and is based upon the physical mechanisms of photon migration in tissues with a particular focus on diffusional wave optics and frequency domain analysis.
2. Discussion of the Prior Art
Imaging of the interior of the human body is of paramount importance in medicine. Current methods are based upon x-rays, nuclear magnetic resonance, ultrasound and other specialized methods which noninvasively provide images of internal anatomical details. Optical imaging in the near infrared has been suggested as an attractive alternative method, Chance, B., et al. Anal. Biochem. 174, 698-707 (1988). However, prior efforts and studies have concentrated on the detection in the time domain of so-called "ballistic photons," i.e., those few photons which travel through the tissues with no scattering. The primary problem has been distinguishing ballistic photons from others which are subjected to several collisions.
Previous studies of coherent light propagation in tissues have concluded that the penetration depth for most animal tissues is generally a fraction cf a millimeter, and that a lack of optical coherence prevents the realization of optical imaging. Several approaches have been proposed to achieve optical image reconstruction of thick tissues (more than a centimeter), but all have met with a singular lack of success.
Patent application Ser. No. 310,404, filed Feb. 13, 1989, for "Method and Means for Parallel Frequency Acquisition in Frequency Domain Fluorometry" is also of interest to the present invention as it discloses an arrangement in which an image intensifier is utilized in association with a camera detector, and the gain of the image intensifier is modulated at an appropriate frequency to obtain a heterodyned output frequency within the bandwidth of the camera detector.